Tungsten (also calledwolfram)[15][16] is achemical element; it hassymbolW (fromGerman:Wolfram). Itsatomic number is 74. It is a metal found naturally onEarth almost exclusively incompounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783. Its importantores includescheelite andwolframite, the latter lending the element its alternative name.
Thefree element is remarkable for its robustness, especially the fact that it has the highestmelting point of all known elements, melting at 3,422 °C (6,192 °F; 3,695 K). It also has the highestboiling point, at 5,930 °C (10,706 °F; 6,203 K).[17] Its density is 19.254 g/cm3,[4] comparable with that ofuranium andgold, and much higher (about 1.7 times) than that oflead.[18] Polycrystalline tungsten is an intrinsicallybrittle[19][20][21] andhard material (under standard conditions, when uncombined), making it difficult towork into metal. However, pure single-crystalline tungsten is moreductile and can be cut with a hard-steelhacksaw.[22]
Tungsten is the only metal in the thirdtransition series that is known to occur inbiomolecules, being found in a few species of bacteria andarchaea. However, tungsten interferes withmolybdenum andcopper metabolism and is somewhat toxic to most forms of animal life.[25][26]
Characteristics
Physical properties
Tungsten rod with oxidised surface
In its raw form, tungsten is a hard steel-greymetal that is oftenbrittle and hard towork. Purified, monocrystalline tungsten retains itshardness (which exceeds that of many steels), and becomesmalleable enough that it can be worked easily.[22] It is worked byforging,drawing, orextruding, but it is more commonly formed bysintering. Sintering is often used due to the very high melting point of tungsten.
Of all metals in pure form, tungsten has the highestmelting point (3,422 °C, 6,192 °F), lowestvapor pressure (at temperatures above 1,650 °C, 3,000 °F), and the highesttensile strength.[27] Althoughcarbon remains solid at higher temperatures than tungsten, carbonsublimes atatmospheric pressure instead of melting, so it has no melting point. Moreover, tungsten's most stablecrystal phase does not exhibit any high-pressure-induced structural transformations for pressures up to at least 364 gigapascals.[28] Tungsten has the lowestcoefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point andtensile strength of tungsten originate from strongcovalent bonds formed between tungsten atoms by the 5d electrons.[29]Alloying small quantities of tungsten withsteel greatly increases itstoughness.[18]
Tungsten exists in two majorcrystalline forms: α and β. The former has abody-centered cubic structure and is the more stable form. The structure of theβ phase is calledA15 cubic; it ismetastable, but can coexist with the α phase at ambient conditions owing to non-equilibrium synthesis or stabilization by impurities. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnarhabit. The α phase has one third of theelectrical resistivity[30] and a much lowersuperconducting transition temperature TC relative to the β phase: ca. 0.015 K vs. 1–4 K; mixing the two phases allows obtaining intermediate TC values.[31][32] The TC value can also be raised byalloying tungsten with another metal (e.g. 7.9 K for W-Tc).[33] Such tungsten alloys are sometimes used in low-temperature superconducting circuits.[34][35][36]
Naturally occurring tungsten consists of four stableisotopes (182W,183W,184W, and186W) and one very long-lived radioisotope,180W. Theoretically, all five can decay into isotopes of element 72 (hafnium) byalpha emission, but only180W has been observed to do so, with a half-life of(1.8±0.2)×1018 years;[37][38] on average, this yields about two alpha decays of180W per gram of natural tungsten per year.[39] This rate is equivalent to aspecific activity of roughly 63 micro-becquerel per kilogram. This rate of decay is orders of magnitude lower than that observed in carbon or potassium as found on earth, which likewise contain small amounts of long-lived radioactive isotopes.Bismuth was long thought to be non-radioactive, but209 Bi (its longest lived isotope) actually decays with a half-life of2.01×1019 years or about a factor 10 slower than180 W. However, due to naturally occurring bismuth being 100%209 Bi, its specific activity is actually higher than that of natural tungsten at 3 milli-becquerel per kilogram. The other naturally occurring isotopes of tungsten have not been observed to decay, constraining their half-lives to be at least4×1021 years.
Another 34 artificialradioisotopes of tungsten have been characterized, the most stable of which are181W with a half-life of 121.2 days,185W with a half-life of 75.1 days,188W with a half-life of 69.4 days,178W with a half-life of 21.6 days, and187W with a half-life of 23.72 h.[39] All of the remainingradioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes.[39] Tungsten also has 12 meta states, with the most stable being179mW (t1/2 6.4 minutes).
Chemical properties
Tungsten is a mostly non-reactive element: it does not react with water, is immune to attack by most acids and bases, and does not react with oxygen or air at room temperature. At elevated temperatures (i.e., when red-hot) it reacts with oxygen to form thetrioxide compound tungsten(VI), WO3. It will, however, react directly with fluorine (F2) at room temperature to formtungsten(VI) fluoride (WF6), a colorless gas. At around 250 °C it will react with chlorine or bromine, and under certain hot conditions will react with iodine. Finely divided tungsten ispyrophoric.[40][41]
The most common formaloxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6.[41][42] Tungsten typically combines with oxygen to form the yellowtungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions,WO2− 4.
Tungsten carbides (W2C and WC) are produced by heating powdered tungsten with carbon. W2C is resistant to chemical attack, although it reacts strongly withchlorine to formtungsten hexachloride (WCl6).[18]
In aqueous solution, tungstate gives theheteropoly acids andpolyoxometalateanions under neutral and acidic conditions. Astungstate is progressively treated with acid, it first yields the soluble,metastable "paratungstate A"anion,W 7O6− 24, which over time converts to the less soluble "paratungstate B" anion,H 2W 12O10− 42.[43] Further acidification produces the very soluble metatungstate anion,H 2W 12O6− 40, after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygenoctahedra known as theKeggin anion. Many other polyoxometalate anions exist as metastable species. The inclusion of a different atom such asphosphorus in place of the two centralhydrogens in metatungstate produces a wide variety of heteropoly acids, such asphosphotungstic acid H3PW12O40.
In gaseous form, tungsten forms the diatomic species W2. These molecules feature asextuple bond between tungsten atoms — the highest known bond order amongstable atoms.[44][45]
History
In 1781,Carl Wilhelm Scheele discovered that a newacid,tungstic acid, could be made fromscheelite (at the time called tungsten).[46][47] Scheele andTorbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[48] In 1783,José andFausto Elhuyar found an acid made fromwolframite that was identical to tungstic acid. Later that year, at theRoyal Basque Society in the town ofBergara, Spain, the brothers succeeded in isolating tungsten by reduction of this acid withcharcoal, and they are credited with the discovery of the element (they called it "wolfram" or "volfram").[49][50][51][52][53]
The strategic value of tungsten came to notice in the early 20th century. British authorities acted in 1912 to free theCarrock mine from the German owned Cumbrian Mining Company and, duringWorld War I, restrict German access elsewhere.[54] InWorld War II, tungsten played a more significant role inbackground political dealings. Portugal, as the main European source of the element, wasput under pressure from both sides, because of its deposits of wolframite ore atPanasqueira. Tungsten's desirable properties such as resistance to high temperatures, its hardness and density, and its strengthening of alloys made it an important raw material for the arms industry,[55][56] both as a constituent of weapons and equipment and employed in production itself, e.g., intungsten carbide cutting tools for machining steel.Now tungsten is used in many more applications such as aircraft and motorsport ballast weights, darts, anti-vibration tooling, and sporting equipment.
It is suggested that remnants of wolfram have been found in what may have been the garden of the astronomer and alchemistTycho Brahe.[60]
Etymology
The nametungsten (which means'heavy stone' inSwedish and was the old Swedish name for the mineralscheelite and other minerals of similar density) is used in English, French, and many other languages as the name of the element, butwolfram (orvolfram) is used in most European (especially Germanic and Slavic) languages and is derived from the mineralwolframite, which is the origin of the chemical symbolW.[22] The namewolframite is derived fromGermanwolf rahm ('wolf soot, wolf cream'), the name given to tungsten byJohan Gottschalk Wallerius in 1747. This, in turn, derives fromLatinlupi spuma, the nameGeorg Agricola used for the mineral in 1546, which translates into English as'wolf's froth' and is a reference to the large amounts oftin consumed by the mineral during its extraction, as though the mineral devoured it like a wolf.[13] This naming follows a tradition of colorful names miners from theOre Mountains would give various minerals, out of a superstition that certain ones that looked as if they contained then-known valuable metals but when extracted were somehow "hexed".Cobalt (cf.Kobold),pitchblende (cf. Germanblenden for'to blind, to deceive') andnickel (cf. "Old Nick") derive their names from the same miners' idiom.
Occurrence
Wolframite mineral, with a scale in cm
Tungsten has thus far not been found in nature in its pure form.[61] Instead, tungsten is found mainly in the mineralswolframite andscheelite.[61] Wolframite isiron–manganese tungstate(Fe,Mn)WO4, a solid solution of the two mineralsferberite (FeWO4) andhübnerite (MnWO4), whilescheelite iscalcium tungstate (CaWO4). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economic value.
Tungsten forms chemical compounds in oxidation states from −2 to +6. Higher oxidation states, always as oxides, are relevant to its terrestrial occurrence and its biological roles, mid-level oxidation states are often associated withmetal clusters, and very low oxidation states are typically associated withCO complexes. The chemistries of tungsten andmolybdenum show strong similarities to each other, as well as contrasts with their lighter congener,chromium. The relative rarity of tungsten(III), for example, contrasts with the pervasiveness of the chromium(III) compounds. The highest oxidation state is seen intungsten(VI) oxide (WO3).[62] Tungsten(VI) oxide is soluble in aqueousbase, forming tungstate (WO42−). Thisoxyanion condenses at lowerpH values, formingpolyoxotungstates.[63]
The broad range ofoxidation states of tungsten is reflected in its various chlorides:[62]
Organotungsten compounds are numerous and also span a range of oxidation states. Notable examples include the trigonal prismaticW(CH3)6 and octahedralW(CO)6.
Production
Tungsten mining inRwanda forms an important part of the country's economy.[64]Tungsten concentrate production, 1946
Reserves
The world's reserves of tungsten are 3,200,000 tonnes; they are mostly located inChina (1,800,000 t),Canada (290,000 t),[65]Russia (160,000 t),Vietnam (95,000 t) andBolivia. As of 2017, China, Vietnam and Russia are the leading suppliers with 79,000, 7,200 and 3,100 tonnes, respectively. Canada had ceased production in late 2015 due to the closure of its sole tungsten mine. Meanwhile, Vietnam had significantly increased its output in the 2010s, owing to the major optimization of its domestic refining operations, and overtook Russia and Bolivia.[66]
China remains the world's leader not only in production, but also in export and consumption of tungsten products. Tungsten production is gradually increasing outside China because of the rising demand. Meanwhile, its supply by China is strictly regulated by the Chinese Government, which fights illegal mining and excessive pollution originating from mining and refining processes.[67]
There is a large deposit of tungsten ore on the edge ofDartmoor in theUnited Kingdom, which was exploited duringWorld War I andWorld War II as theHemerdon Mine. Following increases in tungsten prices, this mine was reactivated in 2014,[68] but ceased activities in 2018.[69]
Within theEU, theAustrian Felbertal scheelite deposit is one of the few producing tungsten mines.[70]Portugal is one of Europe's main tungsten producers, with 121 kt of contained tungsten in mineral concentrates from 1910 to 2020, accounting for roughly 3.3% of the global production.[71]
South Korea'sSangdong mine, one of the world's largest tungsten mines with 7,890,000 tonnes ofhigh-grade tungsten reportedly buried, was closed in 1994 due to low profitability but has since re-registeredmining rights and is scheduled to resume activities in 2024.[74][75]
Extraction
Tungsten is extracted from its ores in several stages. The ore is eventually converted totungsten(VI) oxide (WO3), which is heated withhydrogen or carbon to produce powdered tungsten.[48] Because of tungsten's high melting point, it is not commercially feasible to cast tungsteningots. Instead, powdered tungsten is mixed with small amounts of powdered nickel or other metals, andsintered. During the sintering process, the nickel diffuses into the tungsten, producing an alloy.
Tungsten can also be extracted by hydrogen reduction ofWF6:
Tungsten is not traded as a futures contract and cannot be tracked on exchanges like theLondon Metal Exchange. The tungsten industry often uses independent pricing references such asArgus Media orMetal Bulletin as a basis for contracts.[77] The prices are usually quoted for tungsten concentrate or WO3.[66]
Tungsten is mainly used in the production of hard materials based ontungsten carbide (WC), one of the hardestcarbides. WC is an efficientelectrical conductor, but W2C is less so. WC is used to make wear-resistantabrasives, and "carbide" cutting tools such as knives, drills,circular saws,dies,milling andturning tools used by the metalworking, woodworking,mining,petroleum and construction industries.[18] Carbide tooling is actually a ceramic/metal composite, where metallic cobalt acts as a binding(matrix) material to hold the WC particles in place. This type of industrial use accounts for about 60% of current tungsten consumption.[79]
Thejewelry industry makes rings of sinteredtungsten carbide, tungsten carbide/metal composites, and also metallic tungsten.[80] WC/metal composite rings use nickel as the metal matrix in place ofcobalt because it takes a higher luster when polished. Sometimes manufacturers or retailers refer totungsten carbide as a metal, but it is aceramic.[81] Because of tungsten carbide's hardness, rings made of this material are extremely abrasion resistant, and will hold a burnished finish longer than rings made of metallic tungsten. Tungsten carbide rings are brittle, however, and may crack under a sharp blow.[82]
The hardness and heat resistance of tungsten can contribute to usefulalloys. A good example ishigh-speed steel, which can contain as much as 18% tungsten.[83] Tungsten's high melting point makes tungsten a good material for applications likerocket nozzles, for example in theUGM-27 Polarissubmarine-launched ballistic missile.[84] Tungsten alloys are used in a wide range of applications, including the aerospace and automotive industries and radiation shielding.[85]Superalloys containing tungsten, such asHastelloy andStellite, are used inturbine blades and wear-resistant parts and coatings.
Tungsten's heat resistance makes it useful inarc welding applications when combined with another highly-conductive metal such as silver or copper. The silver or copper provides the necessary conductivity and the tungsten allows the welding rod to withstand the high temperatures of the arc welding environment.[86]
Permanent magnets
Quenched (martensitic) tungsten steel (approx. 5.5% to 7.0% W with 0.5% to 0.7% C) was used for making hard permanent magnets, due to its highremanence andcoercivity, as noted byJohn Hopkinson (1849–1898) as early as 1886. The magnetic properties of a metal or an alloy are very sensitive to microstructure. For example, while the element tungsten is not ferromagnetic (butiron is), when it is present in steel in these proportions, it stabilizes themartensite phase, which has greater ferromagnetism than theferrite (iron) phase due to its greater resistance tomagnetic domain wall motion.
Military
Tungsten, usually alloyed withnickel,iron, orcobalt to form heavy alloys, is used inkinetic energy penetrators as an alternative todepleted uranium, in applications where uranium'sradioactivity is problematic even in depleted form, or where uranium's additionalpyrophoric properties are not desired (for example, in ordinary small arms bullets designed to penetrate body armor). Similarly, tungsten alloys have also been used inshells,grenades, andmissiles, to create supersonic shrapnel. Germany used tungsten during World War II to produce shells for anti-tank gun designs using the Gerlichsqueeze bore principle to achieve very high muzzle velocity and enhanced armor penetration from comparatively small caliber and light weight field artillery. The weapons were highly effective but a shortage of tungsten used in the shell core, caused in part by theWolfram Crisis, limited their use.[citation needed]
Tungsten has also been used indense inert metal explosives, which use it as dense powder to reduce collateral damage while increasing the lethality of explosives within a small radius.[87]
Tungstenoxides are used inceramic glazes andcalcium/magnesium tungstates are used widely influorescent lighting. Crystaltungstates are used asscintillation detectors innuclear physics andnuclear medicine. Other salts that contain tungsten are used in the chemical andtanning industries.[27]Tungsten oxide (WO3) is incorporated intoselective catalytic reduction (SCR) catalysts found in coal-fired power plants. These catalysts convertnitrogen oxides (NOx) to nitrogen (N2) and water (H2O) using ammonia (NH3). The tungsten oxide helps with the physical strength of the catalyst and extends catalyst life.[90] Tungsten containing catalysts are promising for epoxidation,[91] oxidation,[92] and hydrogenolysis reactions.[93] Tungsten heteropoly acids are key component of multifunctional catalysts.[94] Tungstates can be used as photocatalyst,[95] while the tungsten sulfide as electrocatalyst.[96]
Niche uses
Applications requiring its high density include weights,counterweights, ballast keels for yachts, tail ballast for commercial aircraft, rotor weights for civil and military helicopters, and as ballast in race cars forNASCAR andFormula One.[97] Being slightly less than twice the density, tungsten is seen as an alternative (albeit more expensive) to leadfishing sinkers.Depleted uranium is also used for these purposes, due to similarly high density. Seventy-five-kg blocks of tungsten were used as "cruise balance mass devices" on the entry vehicle portion of the 2012Mars Science Laboratory spacecraft. It is an ideal material to use as adolly forriveting, where the mass necessary for good results can be achieved in a compact bar. High-density alloys of tungsten with nickel, copper or iron are used in high-qualitydarts[98] (to allow for a smaller diameter and thus tighter groupings) or forartificial flies (tungsten beads allow the fly to sink rapidly). Tungsten is also used as a heavy bolt to lower the rate of fire of theSWD M11/9 sub-machine gun from 1300 RPM to 700 RPM. Somestring instrument strings incorporates tungsten.[99][100] Tungsten is used as an absorber on the electron telescope on theCosmic Ray System of the twoVoyager spacecraft.[101]
Gold substitution
Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative togold orplatinum.[22][102] Metallic tungsten ishypoallergenic, and is harder than gold alloys (though not as hard as tungsten carbide), making it useful forrings that will resist scratching, especially in designs with abrushed finish.
Because the density is so similar to that of gold (tungsten is only 0.36% less dense), and its price of the order of one-thousandth, tungsten can also be used incounterfeiting ofgold bars, such as by plating a tungsten bar with gold,[103][104][105] which has been observed since the 1980s,[106] or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.[107] The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests.[103]
Gold-plated tungsten is available commercially from China (the main source of tungsten), both in jewelry and as bars.[108]
Electronics
Because it retains its strength at high temperatures and has a highmelting point, elemental tungsten is used in many high-temperature applications,[109] such asincandescent light bulb,cathode-ray tube, andvacuum tube filaments,heating elements, androcket engine nozzles.[22] Its high melting point also makes tungsten suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in thegas tungsten arc welding process (also called tungsten inert gas (TIG) welding).[110]
Tungsten electrode used in agas tungsten arc welding torchTungsten filament is used in incandescent lightbulbs, where it is heated until it glows
Because of its conductive properties and relative chemical inertness, tungsten is also used inelectrodes, and in the emitter tips in electron-beam instruments that usefield emission guns, such aselectron microscopes. In electronics, tungsten is used as an interconnect material inintegrated circuits, between thesilicon dioxidedielectric material and the transistors. It is used in metallic films, which replace the wiring used in conventional electronics with a coat of tungsten (ormolybdenum) onsilicon.[76]
The electronic structure of tungsten makes it one of the main sources forX-ray targets,[111][112] and also for shielding from high-energyradiations (such as in theradiopharmaceutical industry for shielding radioactive samples ofFDG). It is also used in gamma imaging as a material from which coded apertures are made, due to its excellent shielding properties. Tungsten powder is used as a filler material inplastic composites, which are used as a nontoxic substitute forlead inbullets,shot, and radiation shields. Since this element's thermal expansion is similar toborosilicate glass, it is used for making glass-to-metal seals.[27] In addition to its high melting point, when tungsten is doped with potassium, it leads to an increased shape stability (compared with non-doped tungsten). This ensures that the filament does not sag, and no undesired changes occur.[113]
Tungsten is used in producing vibration motors, also known as mobile vibrators.[114] These motors are integral components that provide tactile feedback to users, alerting them to incoming calls, messages, and notifications.[115] Tungsten's high density, hardness, and wear resistance property helps to endure the high-speed rotational vibrations these motors generate.[116][117]
Nanowires
Through top-downnanofabrication processes, tungstennanowires have been fabricated and studied since 2002.[118] Due to a particularly high surface to volume ratio, the formation of a surface oxide layer and the single crystal nature of such material, the mechanical properties differ fundamentally from those of bulk tungsten.[119] Such tungsten nanowires have potential applications innanoelectronics and importantly as pH probes and gas sensors.[120] In similarity tosilicon nanowires, tungsten nanowires are frequently produced from a bulk tungsten precursor followed by athermal oxidation step to control morphology in terms of length and aspect ratio.[121] Using theDeal–Grove model it is possible to predict the oxidation kinetics of nanowires fabricated through such thermal oxidation processing.[122]
Fusion power
Due to its high melting point and good erosion resistance, tungsten is a lead candidate for the most exposed sections of the plasma-facing inner wall ofnuclear fusionreactors. Tungsten, as a plasma-facing component material, features exceptionally lowtritium retention through co-deposition and implantation, which enhances safety by minimizing radioactive inventory, improves fuel efficiency by making more fuel available for fusion reactions, and supports operational continuity by reducing the need for frequent fuel removal from surfaces.[123] It will be used as theplasma-facing material of thedivertor in theITER reactor,[124] and is currently in use in theJET test reactor.
Biological role
Tungsten, at atomic numberZ = 74, is the heaviest element known to be biologically functional. It is used by some bacteria andarchaea,[125] but not ineukaryotes. For example,enzymes calledoxidoreductases use tungsten similarly tomolybdenum by using it in a tungsten-pterin complex withmolybdopterin (molybdopterin, despite its name, does not contain molybdenum, but may complex with either molybdenum or tungsten in use by living organisms). Tungsten-using enzymes typically reducecarboxylic acids toaldehydes.[126] The tungsten oxidoreductases may also catalyse oxidations. The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdopterin-requiring enzymes.[127] One of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterialformate dehydrogenase H) is known to use a selenium-molybdenum version of molybdopterin.[128]Acetylene hydratase is an unusualmetalloenzyme in that it catalyzes a hydration reaction. Two reaction mechanisms have been proposed, in one of which there is a direct interaction between the tungsten atom and the C≡C triple bond.[129] Although a tungsten-containingxanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described.[130]
In soil, tungsten metal oxidizes to thetungstate anion. It can be selectively or non-selectively imported by someprokaryotic organisms and may substitute formolybdate in certainenzymes. Its effect on the action of these enzymes is in some cases inhibitory and in others positive.[131] The soil's chemistry determines how the tungsten polymerizes;alkaline soils cause monomeric tungstates;acidic soils cause polymeric tungstates.[132]
Sodium tungstate andlead have been studied for their effect onearthworms. Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited theirreproductive ability.[133]
Tungsten has been studied as a biological copper metabolicantagonist, in a role similar to the action of molybdenum. It has been found thattetrathiotungstate [zh] salts may be used as biological copperchelation chemicals, similar to thetetrathiomolybdates.[134]
In archaea
Tungsten is essential for some archaea. The following tungsten-utilizing enzymes are known:
Because tungsten is a rare metal[136] and its compounds are generally inert, the effects of tungsten on the environment are limited.[137] The abundance of tungsten in the Earth's crust is thought to be about 1.5 parts per million. It is the 58th most abundant element found on Earth.[138]
It was at first believed to be relatively inert and an only slightly toxic metal, but beginning in the year 2000, the risk presented by tungsten alloys, its dusts and particulates to induce cancer and several other adverse effects in animals as well as humans has been highlighted from in vitro and in vivo experiments.[139][140]Themedian lethal dose LD50 depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbits)[141][142] and 5000 mg/kg (tungsten metal powder,intraperitoneal, rats).[143][144]
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